thirdeye
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Exo and enothermic
I need some help in understand energy transfer.
From what i know when a bond is broken energy is absorbed from the molecule whose bond is broken; released when bonds are formed.
Do covalent bonds differ from this rule?
Another thing: all throughout high school i was taught that when bonds are broken heat is released. this is the exact opposite from what i've
stated before. does anyone know where this comes from???
[Edited on 8-6-2003 by thirdeye]
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vulture
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First of all, forget all the crap about chemistry you've been taught in highschool. Highschool chemistry is full of false assumptions and
shortcuts because there is no time nor demand to explain things properly.
Breaking a bond always requires energy INPUT. Thus this part is endothermic.
Formation of a bond always releases energy. This is exothermic.
In exothermic reactions, the energy required to break to bond is very small compared to the energy to form a new bond, assuming that the new bond is
of lower energy than the first. This way the process can still be exothermic.
Thermodynamics as stated above do apply to all bonds, including covalent and ionic ones.
[Edited on 9-6-2003 by vulture]
One shouldn't accept or resort to the mutilation of science to appease the mentally impaired.
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vulture
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The bonds do not expand! The gas does because the gas molecules achieve a higher kinetical energy, therefore collide more fiercely and thus take up
more space.
One shouldn't accept or resort to the mutilation of science to appease the mentally impaired.
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trogdor
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?
wow i'm confused...i always thought it was exactly opposite.
when you break bonds you release energy.? For example ATP is broken down into ADP+P, and energy is released. (exergonic in in biology) or say
something explodes, its b/c its molecular bonds were broken...so energy is released, and heat is a byproduct making it exothermic
and when bonds are formed, you need an input of energy.
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tom haggen
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Funny vulture. I have been writing papers for my class and have been unintentionally
criticizing the public school system for like 2 weeks. Here is yet another example "First of all, forget all the crap about chemistry you've
been taught in highschool. Highschool chemistry is full of false assumptions and shortcuts because there is no time nor demand to explain things
properly."
N/A
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Polverone
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No
When something explodes, it's exothermic and self-sustaining because the products are more stable (lower energy) than the
reactant(s); the difference in energy between reactants and products is what's released.
For example, methyl nitrate CH3NO3 detonating:
2 CH3NO3 --> CO2 + CO + N2 + 3 H2O
(hmm, is this a realistic picture of the reaction products?)
This reaction is exothermic because CO2, CO, N2, and H2O are more stable than CH3NO3. But it does take some energy to begin the sulf-sustaining
bond-breaking process. This is why methyl nitrate does not explode spontaneously.
PGP Key and corresponding e-mail address
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trogdor
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ty
and there is light...thanks for the explanation.
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t_Pyro
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Another thing that has to be kept in mind is that to initiate a reaction at the molecular level, a collision between the reactant molecules has to
take place with enough kinetic energy for the reaction to be initiated. This is called energy of activation, and has little, or no indication of the
energy change involved with the reaction. An exothermic reaction might have a higher energy of activation than an endothermic one, but once the
reaction is initiated, the energy liberated is far greater than the energy required to initiate it, hence a net evolution of heat. eg. thermite vs
combustion of ethanol
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